Development of dynamic model of cornstalk bale combustion

Abstract: The differential thermal experiments of entire cornstalk bale combustion were designed according to the characteristics of cornstalk bale combustion. A dynamic model of the combustion process was developed through analyzing thermo-gravimetric data collected from the combustion of cornstalk bales under different air supply temperature (18℃-90℃) and different air flow with excess air coefficientαwith 0.7, 1.1 or 1.5. The pyrolysis kinetic parameters modeled include activation energy and frequency factor. The activation energy and frequency factor adopted from Kissinger method were 94.4 kJ/mol and 70.6 kJ/mol, 1.2×106 and 3.3×106 respectively. Their correlation coefficient was greater than 0.99. Model predicted results and measured data were essentially identical. The model performed well. In this experiment the cornstalk bale combustion process were divided as three parts: endothermic and dehydration，precipitation of volatile and the combustion reaction，fixed carbon combustion reaction. The initial temperature of the straw of the volatile gradually decreased with increasing heating rate, volatilization is releasing slowly. First, it reached in kinetic region, gradually into transition region, finally in diffusion region with volatilization combustion. Final temperature of the precipitation of volatile and the peak temperature of the weight loss rate deviated to the side of high temperature. The result showed that the TG and DTG characteristic curve of cornstalk bale combustion were similar overall. The burning velocity changed rapidly in the early period of combustion, it slowed down gradually in the middle period and finally ended towards a stable condition. According to the combustion experiments of cornstalk bales, the higher the combustion temperature was, the faster volatilization separated out. The dominant factors that influenced the combustion efficiency are the combustion temperature and air flow. The controlled temperature combustion under rational air distribution and dissolution velocity of volatiles were uniform and moderate, combustion was relatively stable. The combustion dynamic model provides a theory basis for the design, operation and reconstruction of biomass bale and combustion equipment. It is expected that biomass bale combustion technology will be transferred into real world production .